In recent years, input apparatuses called touch panels have been used for information processing apparatuses such as automatic teller machines in financial institution, ticketing machines in railroad stations, PDAs (Personal Digital Assistants), and so forth. The touch panel type input apparatus correlates icons and so forth displayed on a display such as an LCD (Liquid Crystal Display) with the coordinate system on the display panel and displays the position that the user has touched with his or her finger or a pointing device such as a pen so as to accomplish a GUI (Graphical User Interface) function.
In the conventional touch panel type input apparatus, when the user operates it and inputs data thereto, for example an icon that he or she has pressed varies in its appearance or an operation sound occurs so as to inform him or her that the input operation has been accepted. In contrast, in a recent touch panel, when the user presses an icon or the like, the height of the panel varies, causing a force sense to be fed back to his or her finger or a pointing device. As a result, since the user can feel as if he or she touched (clicked) a switch button, his or her operational feeling improves.
For example, Japanese Patent Application Laid-Open Publication No. 2002-259059 (laid open on Sep. 13, 2002) discloses a resistor film type touch panel having a structure of which a plurality of electrode sheets on which transparent electrodes are formed are layered in such a manner that they are spaced apart by a predetermined length and their electrodes are oppositely aligned. In particular, paragraphs [0037] to [0042] and FIG. 6 describe a touch panel having a multilayer structure, three or more electrode sheets, and actuators such as bobbin coils disposed between a casing that fixes the touch panel and a casing that fixes the display side so as to feed back a force sense to the touch panel.
Piezoelectric actuators that use piezoelectric bi-morph devices are thought to be suitable to accomplish such a force sense feedback function. The piezoelectric actuator has a structure of which a plurality of film-shaped piezoelectric members are adhered through an electrode sheet. The piezoelectric actuator has a characteristic of which when a voltage is applied between both surfaces of the piezoelectric actuator, it curves. Thus, when the actuators are disposed between the casing of the panel side on which touch sensors that detect a touching operation or a pressing operation and the casing of the display side, the panel surface can be moved upward and downward.
Next, with reference to FIG. 13 and FIG. 14, an example of the structure of the conventional touch panel type input apparatus having the force sense feedback function will be described.
FIG. 13 is a perspective view showing an example of the structure of the conventional touch panel type input apparatus that has the force sense feedback function.
As shown in FIG. 13, the conventional input apparatus has a touch sensor portion 102 that covers the display surface of for example a liquid crystal display portion 101. Piezoelectric actuators 103 are disposed between the touch sensor portion 102 and the liquid crystal display portion 101. In the example shown in the drawing, four piezoelectric actuators 103 are diagonally disposed on the upper surface of the liquid crystal display portion 101. In such a structure, the same drive voltage is applied to the piezoelectric actuators 103 so that the entire touch sensor portion 102 is moved upward and downward. Although the piezoelectric actuators 103 are actually disposed between a metal frame of the liquid crystal display portion 101 and a metal frame of the touch sensor portion 102, these metal frames are disposed outside the display area of the liquid crystal display portion 101 and the touch sensor portion 102 and the metal frames are omitted in the drawing.
FIG. 14 is a sectional view showing the mounting structure of the conventional piezoelectric actuator 103.
FIG. 14 shows a cross section viewed from arrow E of FIG. 13. When a drive voltage is applied to the piezoelectric actuator 103, it curves and deforms upward and downward. When the center portion and both the end portions contact and press the touch sensor portion 102 or the liquid crystal display portion 101, the force sense feedback function is accomplished.
However, it is not desired that the piezoelectric actuator 103 directly contract the touch sensor portion 102 and the liquid crystal display portion 101. Conventionally, a plurality of spacers having a predetermined thickness are disposed at a plurality of positions on the upper surface and the lower surface of the piezoelectric actuator 103. In the example shown in FIG. 14, two spacers 104a and 104b are disposed at nearly end portions of the lower surface of the piezoelectric actuator 103 and one spacer 104c at the center portion of the upper surface thereof so that these spacers touch the liquid crystal display portion 101 and the touch sensor portion 102. In this structure, even if the piezoelectric actuator 103 deforms downward, the center portion of the lower surface of the piezoelectric actuator 103 and both the end portions of the upper surface thereof can be prevented from directly contacting the liquid crystal display portion 101.
However, when the piezoelectric actuator is mounted with one upper spacer and two lower spacers, several problems will arise.
The first problem is the accuracy of the thickness of spacers. When the spacers are too thick, since they deform by themselves, force that presses the touch sensor portion is transferred to the piezoelectric actuator. Thus, since the piezoelectric actuator is damaged, the thickness of the spacers cannot be unnecessarily increased. In other words, the spacers need to have a height (for example, 100 μm) so that corresponding to the amount of deformation of the center portion of the piezoelectric actuator, the spacers do not deform against the pressure from the touch sensor portion.
Thus, as spacers, a thin sheet material is used. These spacers are adhered at predetermined positions of the piezoelectric actuator. When a double-sided adhesive tape is used to adhere the spacers, the working efficiency is relatively improved. However, since the double-sided adhesive tape deforms in the thickness direction to some extent, it is difficult to accurately maintain the thickness of the spacers and the double-sided adhesive tape. Instead, when an adhesive agent is used to adhere the spacers to the piezoelectric actuator, the adhering work takes a time and the productivity deteriorates.
When the piezoelectric actuators are wired, the following problem will reside. Normally, the piezoelectric actuators are wired with lead wires. However, lead wires that can be used are very thin. In addition, since lead wires are connected to moving portions, the lead wires tend to break. In addition, lead wires should be carefully routed in a limited space. When lead wires are not fixed for moving portions, they may slip to the display area of the display portion. In addition, since a plurality of piezoelectric actuators are disposed, a plurality of types of piezoelectric actuators that have lead wires of different lengths should be provided corresponding to routing, distance to drivers, and so forth. Thus, the productive efficiency is low.
In addition, when the piezoelectric actuators are directly mounted on the metal frames of the liquid crystal display portion and so forth through the spacers with the double-sided adhesive tape, not only cannot the accuracy of the thickness be maintained, but it becomes difficult to replace the piezoelectric actuators with other ones as a problem with respect to maintenance. Maintenance frames made of plastics or the like may be used to hold the piezoelectric actuators. However, when members such as frames are disposed between the touch sensor portion and the liquid crystal display portion, the efficiency of which the deformation of the piezoelectric actuators is transferred to the touch sensor portion deteriorates. In addition, since new parts are used, the production cost rises. Moreover, the difficulty of the mounting work cannot be lightened.